DAWSONITE TRAPPING: AN OVERLOOKED TEMPORARY BUT EFFECTIVE MECHANISM FOR GEOLOGIC CARBON STORAGE?

Mineral trapping is recognized as the most secure carbon capture and storage (CCS) mechanism to ensure the long-term retention of carbon dioxide following its injection into permeable porous geologic formations. This process can immobilize CO₂ as carbonate minerals, typically as calcite, dolomite, ankerite, and siderite. Under some natural conditions, however, dawsonite (NaAl(OH)₂CO₃) is also stabilized, sometimes attaining significant volume fractions (VF) over 0.2 in some sedimentary formations that may originally have been rich in sodic feldspars.

In this study, we used a dawsonite-rich (~10%) CO₂ gas reservoir in the Hailar basin in northern China as a natural analogue of a CO₂ storage site, along with 2D reactive transport modelling, to demonstrate that a large amount of dawsonite can be generated in sandstone formations, provided sufficient Na-rich feldspar and CO₂ gas are available. Modelling results show that dawsonite mineral trapping is thermodynamically favoured in the Hailar basin. While precipitated dawsonite can be preserved only in a hydrodynamically-closed system in the long term under high CO₂ fugacity and high Na activities in solution, short-term trapping of CO₂ in dawsonite (on the order of 10 kyr) is possible and lowers CO₂ pressure, which mitigates the risk of CO₂ premature leakage to the ground surface or overlying drinking water aquifers. The progressive dissipation of the gas phase CO₂ over time is therefore in part controlled by the re-dissolution of dawsonite. Consideration of reservoirs or saline aquifers favourable for dawsonite formation, significantly increases the number of potential CCS sites globally. Alternating water-and-gas injection regimens could further enhance the precipitation of dawsonite in Na-rich aquifers.